The present invention relates to a cluster ion beam irradiation apparatus and a method for manufacturing magnetic recording head element using the apparatus.
As the wiring in semiconductor devices becomes finer and the areal density in hard disk drives increases, attention is being paid to the gas cluster ion beam as the method for manufacturing semiconductor devices and magnetic recording heads. The gas clusters are several hundreds to several thousands aggregates of gaseous atoms or molecules (hereafter referred to as monomer). A method for generating the gas clusters is described in JP-A-4-354865. The ionized clusters are accelerated by an acceleration voltage, and a work is irradiated with the accelerated ionized clusters. If the cluster collides with the work, the incident energy is distributed to individual atoms forming the cluster. As compared with the monomer ion beam, therefore, irradiation at high density and low energy becomes possible.
It is described in I. Yamada, et al., Materials Science and Engineering, R 34, (2001), pp. 231-295 that the cluster ion beam generated as described above has a feature which is different from the conventional monomer ion beam. For example, if the work is irradiated perpendicularly by the conventional monomer ion beam, surface roughness occurs. On the other hand, if the work surface is irradiated perpendicularly by the gas cluster ion beam, it is possible to make an uneven surface even, owing to the lateral sputtering effect.
If the gas cluster ion beam is used, it is easy to reduce the average surface roughness to 1 nm or less. Furthermore, since the gas cluster ion has a large mass, irradiation at lower speed than the monomer ion is possible even if the same acceleration voltage is given. As compared with the process using the monomer ions, therefore, the milling damage depth can be decreased. Furthermore, due to a nonlinear effect caused by multiple-collision of atoms included in a cluster, a high sputtering rate is obtained.
It is disclosed in T. Aoki, et al., Nuclear Instruments and Methods in Physics Research B 202 (2003) pp. 278-282 that the irradiation effect of the gas cluster ions largely depends on the cluster size. In other words, the depth of the milling damage layer largely depends not only on the energy of the gas cluster ions but also on the size thereof. Here, the size of cluster ions means the number of monomers included in a cluster.
As for the method for measuring the size of gas cluster ions, there are methods using a quadrupole mass spectrometer (QMS) and methods using the time of flight (TOF) mass spectrometry. They are disclosed in I. Yamada, et al., Materials Science and Engineering, R 34, (2001), pp. 231-295. Ions having such a mass that the ions can pass through between the rods are determined according to the condition of the high frequency voltage applied to four rods. The methods using the QMS are methods for conducting the mass spectrometry by using this fact.
On the other hand, the TOF mass spectrometry is a method for conducting the mass spectrometry by measuring the time taken for ions to pass through a drift tube, because ions having definite energy have different velocities depending on the mass. As a method for conducting ion mass spectrometry besides the QMS mass spectrometry and the TOF mass spectrometry, a magnetic sector type mass spectrometer using the fact that the Larmar radius differs depending on the momentum of the ion when the ion conducts a Larmar motion is known. In addition, a method by which ion energy and mass can be analyzed simultaneously by combining an electrostatic energy analyzer with the QMS is disclosed in JP-A-11-250854 and another method by which ion energy and mass can be analyzed simultaneously by combining the magnetic sector type mass spectrometer and the TOF method is disclosed in JP-A-2002-15694.